<html>
  <body>
    <canvas id="canvas" width="500" height="500"></canvas>
    <script>
      const canvas = document.getElementById('canvas');
      const ctx = canvas.getContext('2d');
      ctx.fillStyle = 'rgb(0, 255, 0)';
      ctx.fillRect(0, 0, 500, 500);
    </script>
  </body>
</html>
